/Engine/Plugins/Online/OnlineFramework/Source/Party/Public/SocialManager.h
void JoinParty ( const [USocialUser](API\Plugins\Party\User\USocialUser) & UserToJoin, const [FOnlinePartyTypeId](API\Plugins\OnlineSubsystem\FOnlinePartyTypeId) & PartyTypeId, const [FOnJoinPartyAttemptComplete](API\Plugins\Party\USocialManager\FOnJoinPartyAttemptComplete) & OnJoinPartyComplete, const [FName](API\Runtime\Core\UObject\FName) & JoinMethod )